Cannibals great and small

Quasars and binary stars both fuel large outputs of radiation via binges of …

We'll start with the small-scale cannibals first, in this case low-mass neutron stars, which pack a bit more mass than the sun into an area the size of a large asteroid. In cases where these have a normal star as a companion, they tend to strip gas and draw it into a disk-shaped cloud. Their intense gravity then causes this cloud to emit X-rays as its drawn into the neutron star. Scientists had been puzzled by the fact that some of these clouds "blinked" on and off, but new observations from the ESA's XMM-Newton satellite have clarified things a bit. The XMM-Newton was able to determine that some of the X-ray emissions came from fully ionized iron, which let them know that the disk was much hotter than had been expected. Given a hot cloud, computerized models could then generate the blinks.

Meanwhile, using a different observatory (NASA's Chandra) and looking at a different scale (galaxy-sized), new research has provided what may be a glimpse of early stages in the formation of a quasar, the most energetic light source in the universe. These objects are thought to be powered on when a galaxy with a large central black hole collides with a separate galaxy. Under these circumstances, the black hole would receive a sudden influx of gas, which it would use to produce quasar-sized cosmic fireworks. Chandra's spotted X-ray sources at a distance from the active core of the quasar that appear to be the result of a massive shock wave impacting upon the gas within the galaxy. The most likely source of this shock wave? The ignition of the quasar itself. These observations may give us a better understanding of quasar ignition, and provide us with some hints of what to look for when trying to spot events even closer to the point of ignition.